Perpendicularity 1

[metaldork]

Can anyone please clarify if a perpendicularity call out is controlled by a basic dimension or not? In other words is the tolerance zone centered on a basic dimension?

 

[fsincox]

Sure ideally all should be controlled, that is right out of the book. Frank

 

[CheckerHater]

Actually both (or all three?).
I feel like using direct dimensioning may create ambiguity here. There is a reason ISO calls it "two-point dimension".
(See my post about using Profile)

 

[CheckerHater]

Frank,
Off-topic, but since you brought it up; have you ever seen round hole dimensioned to the edge rather than center?
I did, I was even forced to do it myself, I still don't like it.

 

[fsincox]

CH,
Are you kidding? I cut my teeth on that. It is what I was looking to GD&T to help me escape from.
This thread has confused me a bit with the whole perpendicularity zone centered, center implies a location. Seems like at least part of the perpendicularity zone must be in the location tolerance zone or you would just move it.
Frank

 

[bxbzq]

So, when used together with position requirement, perpendicularity only makes sense when perp. tolerance zone is smaller than position tolerance zone, and both tolerance zones overlap at least partially. To me it means "refinement".

When perpendicularity used together with position, isn't the effect same as a composite positional tolerancing with primary datum repeated in lower segment when the toleranced FOS perpendicular to primary datum?

 

[CheckerHater]

To bxbzq:
It is very close to say the least.
There was also discussion(s) here about using position to single datum to control perpendicularity.

 

[fsincox]

Or as say a refinement of a profile control, like an over all profile.
J-P and Evan are talking about a much more basic level if the are no other controls applied. In theroy those parts are OK, I would not want to walk in court and claim I made a part like CH drew to meet pmarcs ealier print to a judge, he would throw me out of the room until he was instructed in the "letter" of the law.
Frank

 

[Belanger]

Somehow this thread got confused -- I might have had something to do with that of course

CH, pmarc's sketch was right on. The size dimension has absolutely nothing to do with the angle of the sides to the bottom. That's all we were saying.

I think Evan was saying earlier that SOME of the perpendicularity zone can go outside of the location zone. However, since the part must meet both tolerances, that just leaves less of a zone for the actual surface to fall into.

Bxbzq: It's not quite the same as composite position because the lower segment of composite position tolerance also controls the location of the features to each other. A perpendicularity symbol can't do that.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[axym]

CH,

In your hypothetical situation, I would suggest that the part should be rejected. In the report, I would list the Perpendicularity tolerance as conforming and the Position tolerance as nonconforming.

I would agree that in order for the part to conform to both tolerances, the Perpendicularity zone and the Position zone must have at least partial overlap. I just see this as different than the zones' constraints relative to the datum reference frame. The Perpendicularity zone is allowed to freely translate relative to the DRF, the Position zone is not.

This approach allows me to think about each tolerance individually, without regard to the conformance/nonconformance of other tolerances on the same feature. Once everything has been evaluated, the part is accepted if every tolerance conformed and rejected if at least one tolerance didn't conform.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dtmbiz]

Is the fig from CH drawn as produced or are you intending to start with a trapazoid. If I choose that it is a produced version of pmarc's original figure; in that case the perpendicularity between the opposing surfaces must be within the limits of size. Rule #1 applies so at MMB the opposing surface must be perfect form. The most out of parallel would be .2.

There are 3 features of size involved in the figure; width, length, and thickness.

There could be a possible need to "refine" orientation depending on what the default angularity tolerance is. It is difficult to accurately determine or discuss orientation controls and their impact without the rest of the influencing dimensions and controls.

My main point is that the perpendicularity is impacted by size limits and the rule #1 to a degree. I am not sure where the idea that perpendicularity floats outside of the size limits comes from. I would agree that a MMB there would need to be a "refinement" of orientation because there should be at least a default general angularity tolerance. Without an additional perp countrol the orientation tolerance is dictated by the angularity tolerance. So the perpendicularity is controlled by size limits, rule #1, and the angularity tolerance which has not been discussed so far.

Rule #1...

When specifying a form tolerance,
consideration must be given to the control of form
already established through other tolerances such as
size (Rule #1), orientation, runout, and profile controls.

It would be a stretch to say there is positioning in this simple figure....

"Position is the location of one or more features of size
relative to one another or to one or more datums. A positional
tolerance defines either of the following:
(a) a zone within which the center, axis, or center
plane of a feature of size is permitted to vary from a true
(theoretically exact) position
(b) (where specified on an MMC or LMC basis) a
boundary, defined as the virtual condition, located at the
true (theoretically exact) position, that may not be violated
by the surface or surfaces of the considered feature
of size.
Basic dimensions establish the true position from
specified datums and between interrelated features. A
positional tolerance is indicated by the position symbol,
a tolerance value, applicable material condition modifiers,
and appropriate datum references placed in a feature
control frame."

 

[fsincox]

dtmbtz,
I think the AME adds a new element of uncertainty to FOS features now.
Frank

 

[pmarc]

I am referring to my sketch again.
The values of perpendicularity callouts specified on the print can be whatever - even infinity - because size dimension 9.9-10.1 has no influence on orientation of block's width relative to the bottom of the part.

However the measured (actual) values of those perpendicularity errors cannot differ more than 0.2, otherwise I see no chance that limits of size for the width (two-point measurements and rule #1) will be met together with both perp requirements.

Side note: I agree that using basic width plus profile callouts on both sides would make it easier to read, though I do not think my dimensioning scheme creates ambiguity - it is simply less common.

 

[CheckerHater]

pmarc,
"ambiguity" is not a swear word - it just means different interpretations are possible

 

[fsincox]

pmarc,
Your method is still much more common around where I work.
Frank

 

[dtmbiz]

6.3.3 Perpendicularity
Perpendicularity is the condition of a surface, feature’s
center plane, or feature’s axis at a right angle to a
datum plane or datum axis. See Fig. 3-1.

To say that a perpendicularity control can be a tolerance zone that can be infinite is to lose sight of the meaning of perpendicular. When the tolerance zone approaches the point that the right angle becomes something other than 90 degrees then it is no longer perpendicular. At best a tolerance zone could only result in an angle that approaches 90 degrees. At some point it would then be considered parallel to the referenced datum and it certainly wouldn’t be perpendicular.

Much earlier than when a tolerance zone allows the surface to approach 90 degrees, the part’s design intent and mating condition would need to be evaluated as to whether or not the perpendicularity callout is proper or whether and a angularity control would be sufficient. Does the part really need to be a rectangle?

2. The dimension shown across the width of a simple rectangle is to the opposing surfaces not two corner points. Basic drafting 101.

3. The introduction of Rule #1 into the thread was to refocus on the design intent. To focus on one dimension and one control without looking at the whole picture is not productive. Appling the GD&T fundamentals of function and relationship is an exercise in considering the importance and relationship of all features and their dimension’s and geometric controls that capture the design intent.

Will the part function and be cost effective?

 

[CheckerHater]

Sorry,
I never had a chance to take Drafting 101; so could someone direct me to the place in standard where distinction between point-to point, edge-to-edge and plane-to-plane dimensions is made.
(Genuinely curious, only tiny bit of trolling )

 

[Belanger]

CH, I think it boils down to "actual local size" vs. "actual mating envelope." So check out these paragraphs: 1.3.25, 1.3.54, along with all of 2.7.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[dtmbiz]

Let’s start with the fundamental rules...

(i) A 90” angle applies where center lines and
lines depicting features are shown on a drawing at
right angles and no angle is specified. See para.
2.1.1.2.

Notice the word lines and not points?
Can you have a point at a right angle?

(j) A 90” basic angle applies where center lines
of features in a pattern or surfaces shown at right
angles on the drawing are located or defined by basic
dimensions and no angle is specified.

Notice the word "surfaces" and not "points"...

or how about ASME Y14.2

2.3 Visible lines
Visible lines consist of solid lines and shall be used for representing edges or contours.

Can you show me the mathematical standard were 2+2=4?

or how about the mathematical standard for definition for a square, rectangle, cylinder, diameter, radius, right triangle etc; geometric relationships in general...

How does one create a mechanical engineering drawing without having basic drafting 101.... you realize that "101" is a
colloquialism for fundamental drafting....

Actually did have an engineering college student in a CAD class that asked me what a radius was.

Problem is that many folks never had drafting 101...
and don’t forget logic and common sense... which aint too common anymore....

What would be the logic of that dimension being to the "corner points"? If one really needed to identify the dimension "points" they could be identified as points. This would be the exception not the norm.

Maybe this is a parallelogram or trapezoid in disguise and you just fooled me...

 

[CheckerHater]

Thank you JP,
This is not exactly what I asked, but good start.
Does any inside/outside dimension automatically define FOS, or is there something else to it?
And if it is not in/out, then how to measure "non-envelope" dimension?

 

[CheckerHater]

dtmbiz,
You said it yourself, "Visible lines consist of solid lines and shall be used for representing edges or contours". On the drawing we dimension between lines, not surfaces.
Also, I have nothing against angles. Never mentioned angle between points.
And guess what, there are definitions for square and the rest of the gang. Taking Math 101 before drafting actually helps a lot.
And when it comes to college students; worked with one who didn't know how many millimeters are in one inch.
This is why I am leaning towards exact definitions rather than common sense. If common sense existed, nobody would ask for it.